Oscillograph



OSCILLOGRAPH I Filed Aug. 15 1931 2 Sheets'-Sheet 1 INVENTOR JOHN A, MAURER JR. BY 7M M1/GO ATTO R N EY Aug. 28, 1934. J. A. MAURER, JR

OSCILLOGRAPH Filed Aug. l5, 1931 2 Sheets-Sheet 2 u Patented Aug. 28, 1934 OSCILLOGRAPH John A. Maurer, Jr., New York, N. Y., assigner to Radio Corporation of America, a corporationof Delaware Application August 15, 1931, serial No. 557,408

9 claims. (ci. r11- 95) This invention relates to apparatus for recording electrical impulses such as those of audio frequency, and has for its principal object the pro` 'vision -of an improved recording device of the galvanometer type suitable for use-in connec- ,tion with the production'of 16 mm. sound records and the like.

Various types of apparatus have beenv provided f' in the' past for recording electrical impulses modulated in accordance with sound. Many of these devices have been complicated in structure, have required delicate adjustment after assembly, have not been altogether satisfactory and uniform in their operation and have involved comparatively high manufacturing `costs.l The objects realized by the present invention are cheapness in manufacture, automatic centering of the movable parts so as to eliminate the neces- 'sity of delicate adjustment, and uniformity of performance., These results are largely eifected 'by reducing the number of parts to a minimum and so constructing them that when they are assembled they are all held rigidly in predetermined spacial relation, by an improved mounting whereby the Vfragile parts of the device are protected from injury during assembly and are supported in such manner as to give maximum stability, by the omission'of damping materials, such as rubber which deteriorates with use, and by various other features .which are described in the following description.`

My invention will be better understood from the following description when considered rin connection with the accompanying drawings, and its scope will be pointed outA in the appended claims.

yReferring to the drawings:

Fig. 1 illustrates a galvanometer recorder wherein the invention has been embodied, and

Fig. 2 is an exploded view of this recorder.

'Ihe Yrecorder includes a base 10 uponwhich. is

mounted a supporting block 11, the supporting block 11 being attached to the basev by means of screws 12. The pole pieces 13 and 14 are surrounded by exciting coils 15 and 16 respectively -nd are bifurcated at their upper ends to form respectively' extensions 17 and 18, and 19 and 20.

Surrounding the extensions 18 and 20 are the 28 and 29 for determining its spacing from the member 25 and with an extension 30 for adjusting its position after assembly '1n a manner hereinafter described.

In assembling the armature and its support, the extensions 28 and 29are placed against member 25 and the armature is clamped atits upper end by means of clamping block 31 and screw 32 and at its lower end by means of clamping' block 33 and screw 34. With the pole pieces 13 and 14 and various coils assembled as illustrated in Fig. 1 the armature assembly lis readily attached to the pole pieces by sliding the armature 23 be-l tween the ,extensions 17 and 18 and the extensions 19 and 20 of the pole pieces, the support 70v member 25 being attachedrto the pole piece 13 by a lug 35 arranged to cooperate with the screw 36 and to the pole piece 14 by means of a lug v37 and screws 38 and 39.. e

It will be understood that the distance bel tween the lugs 35 and 37 is held within narrow limits and that the spacing of the lugs 26 and 27 with respect to the lugs 35 and'37 is such as to ensure proper alignment of the armature between the pole pieces when the apparatus is completely assembled. As previously indicated the lugs 28 and 29 are utilizedV to ensure the proper spacing` of the armaturevfrom the support` 25. 'Ehe dis` tance from the backs of the pole pieces 13 and 14 to the pole faces of the extensions 17"to 20 85 as related to the center of the pole structure is minus one-half the thickness of the armature and the length of the air gap, Under these conditions, when the` parts are assembled the armature will be located centrally between the pole pieces with an error of the order likely to occur in good machine work, lthat is, notmore than .0005 inch.' This degree of accuracy is sulcient to give satisfactory operation.

The operation of the apparatus will be readily 1 understood without detailed explanation. When no current is transmitted through the signal coils 21 and 22, the armature 23 is in the position illustrated and the light reected from the mirror 24 isfstationary; Under these conditions 100 the flux produced by the coils 15 and 16 produces no torsional effect upon the armature 23 for the reason that the opposite ends of the armature are subject to ux of the same value. When signal current is supplied tothe coils 21 and 22 however, m5 the resultant flux is unbalanced for the Breason that the signal current ux is in the same direction as the exciting flux at one end of the armature and is opposed to the exciting flux at the other end of the armature. This-:unbalance inuo the ux, as Will be readily understood, applies to the armature a torsional force which is modulated in accordance with the signalP current, and the mirror 24 is moved accordingly,

The armature 23 may be made of steel about .014 inch thick and may be about 1% of an inch square. The stems 40 and 41 give the structure the necessary amount of resilience and if the vnatural vibration period of the system is to be 4,000 cycles or above may have a; width of about 25 mils. The mirror 24 may be about 2 millimeters square and is cemented to the armature member, the part of this member to which it vis attached being about 1/8 inch wide. Since the moment of inertia of each of these parts is proportional to the cube of the width, the contribution of this mirror support strip to the total moment of inertia is less than 1/4 the total, which is not serious.

As previously indicated, no damping material such as rubberwhich is likely to deteriorate with use is included in the construction. This is made 'possible by the high flux density produced inthe pole members by the coils 15 and 16. With the described construction, the eiiiciency is suiiiciently high that the motional impedance at resonance, reiiected into the electrical circuit, appears as a resistance term of the order of three times the low frequency impedance of the device, and this increase in electrical impedance acts to limit the current so that resonance is not excessive. In practice when the device is operated from a source of the proper impedance, the reasonance peak is of the order of twice the average ampli.

tude.

The coils 15 and 16 are connected in series and may be supplied with a current of .1 ampere at 5 volts or by a current of 1/3 ampere at 11AA volts depending on the characteristics of `the winding.

- The latter value has the advantage that the field winding may be connected in series with the recorder lamp used in conjunction with it.

The signal coils 21 and 22 may consist of 200 or 300 turns of iine wire, for example, number 36. The impedance at frequencies remote from resonance is mostly inductance, hence there is no point in attempting to keep the resistance of the winding low. In fact it is desirable to make the direct current resistance-about equal to the inductive reactance at about 2,000 cycles. Other- -wise the device will show a falling amplitudefrequency characteristic at frequencies below resonance when fed from a constant voltage source. If the signal windings have the characvteristics indicated above, the signal supply should 'have an impedance of from 15 to 30 ohms.A

The projection30 on the armature member is provided for slight adjustments in the position of the armature 23 after the apparatus has been assembled. When the apparatus is first assembled the armature 23 is centralized as far as average distance from the pole pieces is con` cerned, but it usually has a twist which causes it to lie at an angle with the faces of the pole extensions 17 to 20. By pushing the lug 30 to one side or the other, the support member is readily adjusted to the proper position. It is f merely necessary to push the lug in a direction opposite to that of the observed shift of the light beam reflected from the mirror 24 when the field is applied until an.adjustment is reached such that the light be no longer shifted when the field is put on or oif. Once this condition of stability is obtained, the system continues to function satisfactorily. Experience has shown that the application of signals ten times as great as the normal recording amplitude produces no permanent set of the armature.

Having thus described my invention and the operation thereof, what I claim is:

1. An oscillograph including magnetic pole pieces, and a unitary assembly comprising a sup- .port and an armature member clamped to said support at both of its ends so that the armature portion of said member lies between the pole faces. I

2. An oscillograph including magnetic pole pieces, a unitary assembly comprising a support and an armature member rigidly attached to said support at bothof its ends so that the armature portion of v4said member lies between the pole faces, and means integral with said member for adjusting the position of said armature with respect to said faces. l

3. An oscillograph including magnetic pole pieces, a unitary assembly comprising va support and an armature member rigidly attached to said support at both of its ends, said support being so shaped that the armature portion of said member lies between the pole faces when said support is attached to said pole pieces.

4. An oscillograph including magnetic pole pieces, a unitary assembly comprising an armature member and a support attached to said pole pieces and supporting the armature portion of said member between the pole faces, and means integral with said member for spacing said armature from said support in a direction parallel with said faces.

5. An oscillograph including an integral member comprising an armature portion, a portion for spacing said armature from its support, a resilient portion for permitting vibration of said armatureportion, and a portion for adjusting the position of said armature about its axis.

6. An oscillograph including an integral member composed of a single piece of material comprising an armature, means for spacing said armature from its support, resilient means for permitting vibration of said armature, means for adjusting the position of said armature about its axis, and means for supporting a light controlling surface.

7. An oscillograph including a pair of pole pieces, and a unitary assembly comprising an armature member and a support arranged to be attached to said pole pieces and to protect said member from contact with said pieces during the attachment of said member to said pole pieces.

8. An oscillograph including a pair of pole pieces, a unitary assembly comprising an armature member and a support arranged to be attached to said pole pieces and to protect said member from contact with said pieces during the attachment of said member to said pole pieces, and means adapted to produce a substantially constant iiux in said pole pieces.

9. An oscillograph including a pair of pole pieces, a unitary assembly comprising an armature member and a support arranged to be attached to said pole pieces and to protect said member from contact with said pieces during the attachmentof said member to said pole pieces, means adapted to produce a substantially constant flux in said pole pieces, and means for lmodulating said iiux in accordance with the im- 

